The design of modern scientific experiments requires the control and monitoring of many parallel data streams. However, the serial execution of programming instructions in a computer makes it a challenge to develop software that can deal with the asynchronous, parallel nature of scientific data. Here we present Bonsai, a modular, high-performance, open-source visual programming framework for processing data streams. We will describe Bonsai’s core principles and architecture while specifically highlighting some of the applications that were developed during one year of use in an active neuroscience research institute.